'Triple Bomb' Cyclone Slams West Coast, Killing 2, Soaking Millions

SAN FRANCISCO — Powerful winds from a major "bomb cyclone" claimed at least two lives and knocked out power for more than half a million people overnight in the Pacific Northwest.

The storm system fueled gusts from Seattle to Nothern California, prompting a rare hurricane wind warning off Oregon's coast, and drew some of its strength from an atmospheric river currently drenching much of the West Coast, according to the New York Times.

Also called bombogenesis, bomb cyclones form when warm and cold air masses collide over the ocean and air pressure drops 18 to 24 millibars over 24 hours. At peak strength Tuesday night, the cyclone's central pressure dropped more than three times the threshold, the San Francisco Chronicle reported, qualifying as "triple bombogenesis" and making for the strongest storm on record in that part of the Pacific.

While forecasters expected the cyclone to stay hundreds of miles offshore, The Seattle Times reported it worked like a vacuum Tuesday, siphoning air and quickly intensifying easterly winds over land.

According to the National Weather Service, a buoy off the coast of Vancouver Island recorded a peak gust of 101 mph at 6 p.m. Over the next hour, the weather service reported wind gusts as high as 77 mph at Mount Rainier, 55 mph at the Seattle-Tacoma International Airport, and ranging from 45 to 55 mph in the Seattle metro.

Falling trees were responsible for at least two deaths, authorities said, including a woman in her 50s who was killed when a large tree fell on a homeless encampment in Lynnwood, 16 miles north of Seattle. During the same hour, a woman was killed when a tree fell on her house as she showered in her Bellevue home, roughly 13 miles east of Seattle.

Storm-related power outages unfurled across the region throughout the evening, leaving more than 640,000 customers without power Wednesday morning in Western Washington. More than 114,000 were without power in Seattle, marking the Emerald City's largest outage since a 2006 storm that killed 14 people.

Some utility districts warned customers it could take several days to get all of the lights back on.

Lingering outages prompted all schools to close in two dozen cities in the Puget Sound region.

Meteorologists expected the cyclone would begin dissipating Wednesday but warned a second low-pressure system was on its heels that showed the potential to develop into another bomb cyclone.

Early North Bay rain totals exceed expectations; widespread Bay Area downpours forecast Friday

Influenced by the powerful cyclone, atmospheric rivers were forecast to pour up to 16 inches of rain over southwestern Oregon through Friday, with more than 10 inches possible in parts of Northern California.

Generally, the weather service predicted 5 to 12 inches of rainfall in the North Bay through Sunday, with rain totals ranging from 1 to 6 inches possible in communities south of the Golden Gate Bridge.

The downpour was underway Wednesday morning in the North Bay, where rain totals ranged from 1 to 3 inches by late morning and outpaced earlier predictions, the San Francisco Chronicle reported.

Updated forecasts predicted 7 to 10 inches of rain in the North Bay's coastal ranges through Friday, and up to 15 inches of rain in Cloverdale. Petaluma and Santa Rosa were included in an area classified at slight risk for flash flooding Wednesday and Friday, and a flood watch in place for Sonoma, Napa and Marin counties has been extended until 4 a.m. Saturday.

While the heaviest rain and largest flood threats are in the North Bay, the weather service said the rest of the Bay Area can expect strong downpours Friday. San Francisco was forecast to receive 2-3 inches of rain through Friday, with 1 to 2 inches likely elsewhere in the Bay Area.

According to the weather service, gusts up to 50 mph will be possible across much of the region through Thursday morning. A wind advisory will remain in effect until 6 a.m. Thursday for San Francisco, the entire San Francisco Bay Shoreline and Peninsula coast, and across Marin, Sonoma and Napa counties.

Forecasters warned the combination of heavy rain and strong winds would increase the risk of falling trees, power outages and related hazards.

In the mountain passes, a winter storm warning will remain in place until 10 p.m. Wednesday, where 10 to 20 inches of snow was forecast to fall over the Sierra from Interstate 80 northward.